The present invention relates in general to electrical control systems and in particular to an apparatus for logically combining, synchronizing and distributing event detection signals for triggering purposes.
Electrical control systems typically employ sensors to produce digital indicating signals on detection of various external evehts. The indicating signals are then logically combined to produce triggering signals to control triggerable devices. Complex systems typically employ many such event detectors to provide the necessary information to control many such triggerable devices. Often, however, it is not possible to locate the event detectors and the trigger circuitry in the same equipment module, such as a circuit board, and in complex systems extensive wiring between equipment modules is often required to interconnect event detection and trigger control circuitry. Further, events and triggers are often synchronous signals within an equipment module, with each module having its own independent clock, and it is often difficult to synchronize events and triggers associated with different modules.
Multiplexing systems have been developed to reduce the amount of control circuitry whereby control signals appearing at many locations in one equipment module have been converted to serial data for transmission over a single wire pair to remote equipment modules. Such multiplexing has been effective particularly in reducing interpanel wiring between equipment racks in large control systems. However, parallel-to-serial multiplexing systems typically employ complex circuitry, do not lend themselves to interconnecting triggering signals between small equipment modules and are unsuitable for high speed operation.
What is needed is a means for logically interconnecting event detectors and triggerable devices in a control system which minimizes the amount of interconnecting wiring and which provides for synchronization of differently clocked events and triggers.